Radiotherapy (also known as Radiation Oncology and Radiation Therapy) is generally used as part of cancer treatment to control or kill malignant cells. Radiotherapy makes use of ionizing radiation which, damaging the DNA of exposed tissue and thereby leading to cellular death. The radiation can be delivered by a machine outside the body (external beam radiation therapy) or it can come from radioactive seeds placed into or near the tumor (internal beam radiation therapy, more commonly called brachytherapy).
External beam radiation therapy is the most frequently used form of radiotherapy and is delivered using a linear accelerator (LINAC). The linear accelerator uses microwave technology to accelerate electrons and then allows these electrons to collide with a heavy metal target. As a result of the collisions, high-energy x-rays are produced from the target. These high energy x-rays are shaped as they exit the machine to conform to the shape of the patient's tumor and the customized beam is directed to the patient's tumor.
The patient lies on a moveable treatment couch and lasers are used to make sure the patient is in the proper position. The beam comes out of a part of the accelerator called a gantry, which can be rotated around the patient. Radiation can be delivered to the tumor from any angle by rotating the gantry and moving the treatment couch. During treatment the radiation therapist continuously watches the patient through a closed-circuit television monitor. There usually is also a microphone in the treatment room so that the patient can speak to the therapist if needed. Imaging tools are checked regularly to make sure that the beam position doesn't vary from the original plan.
For effective operation of the radiotherapy system, it is necessary to include a margin of normal tissue around the tumor to allow for uncertainties in daily set-up and internal tumor motion. These uncertainties can be caused by internal movement, e.g. due to respiration. In image guided radiotherapy (IGRT), two and three-dimensional imaging is used to help better deliver radiation therapy to cancerous tumors. In, e.g., “Current concepts on imaging in radiotherapy” by Lecchi et al, MRI, PET or CT images are used for monitoring breathing motions. The article discloses three approaches for dealing with these breathing motions. In one approach, the patient is asked to hold his breath during treatment delivery for obtaining a static tumor position. When using respiratory gating, CT images are used for making it possible to only deliver treatment during well defined parts of the breathing cycle. The third approach is tumor tracking in which the 4D image data (3D+time) is used for making the treatment beam follow the tumor.
Extensive changes in body position can even cause session disruption, thereby hindering the radiotherapy workflow. Body position changes (posture/movements) can occur both voluntary and involuntary. Examples of involuntary changes include respiration (i.e., we breathe often without thinking about it), restless legs and the fact that office workers behind a PC frequently “worsen” (and then correct again) their posture throughout the day. Currently, preventive measures for patient movement/posture in radiotherapy include patient-staff communication (prior to radiotherapy, a patient is told or reminded that lying still is important) and physical support (e.g., head rest, knee rest).
Despite the preventive measures, body position related session disruption, e.g., due to patient anxiety, is a frequently reported problem in radiotherapy. For instance, Clover et al (“Disruption to radiation therapy sessions due to anxiety among patients receiving radiation therapy to the head and neck area can be predicted using patient self-report measures”, Psychooncology, 2010) recently found that anxiety-related session disruption occurs in a substantial amount of radiotherapy patients: 11% duration baseline session and even 24% during treatment session 1.
In addition, a radiotherapy specific problem is that, during radiation, the LINAC gantry circles around the patient while the patient remains at steady position on the bed. This can trigger patient motion in different ways. Motion in the patient's visual field can cause a perception of self-motion (a phenomenon known as “vection”). Vection, in turn, can cause compensatory movements and anticipatory movements. In addition, vection can lead to motion sickness (“vertigo”), can also trigger undesirable patient motion. Particularly elderly persons are susceptible to vection-based self-motion.